Laminated sheet



50 corresponding Patented Jan. 5, 1937 UNHTED STATES PATENT QFFlCE LAMINATED SHEET Kurt Ripper, Berlin-Lichterfelde, Germany No Drawing. Original application March 5, 1931.

- Serial No. 520,478.

Divided and this applica-' tion September 17, 1932, Serial No. 633,685. In Austria December 15, 1930 6 Claims.

My invention relates to laminated sheets or plates of material bonded together in its final 'hardened condition, by condensation products of thiourea or mixtures of thiourea and urea, with formaldehyde. This application is a division of my pending application for a process of making the said condensation products, Serial No. 520,478,

filed March 5, 1931, and for a moldable composition containing the said product.

The object of the present invention primarily is to enable laminated bodies (particularly of paper,

tissue or asbestos) of beautiful aspect and showing excellent mechanical and electrical properties, to be produced.

The process of making the above mentioned condensation products which are exceedingly well suited for being used as agglutinant or impregagent in manufacturing laminated sheets, consists essentially in reacting without applying heat with less than 2 mols, preferably 1 mols, of formaldehyde upon 1 mol. of thiourea or of a mixture of thiourea and urea at a higher hydrogen ion concentration than corresponds to-the value pH=5, consequently at a pH greater than 25 equivalent to 5. Preferably the hydrogen ion concentration is adjusted so as to correspond to. the 'value pH=3. Hydrogen-ion concentration is also sometimes expressed as Cn, using numbers with minus exponents to indicate the actual concentration of hydrogen ions in the solution or aqueous medium. The relationship between Ca and pH is as follows:

Hence, Cn=1 is expressive of the same hydrogen;-ion.concentration as pH- -.5; and (311:" is equivalent to pH=3.

By reacting in the cold with formaldehyde upon 'urea 'at a hydrogen-ion concentration greater than equal to pH 5, a white insoluble product' serving no useful purpose is generated (of. e. g.- Beilstein-Prager-Jacobson, Handbuch der Or-- ganischen Chemie, 3rd edition 1921', Tome IV.

page 48) Thus for instance a solution of 60 parts 45 by weight (1 mol.) of urea in 150 parts by weight of an aqueous formaldehyde solution containing 30% by weight (1% mols) of formaldehyde,

which by the addition of phosphoric acid hadbeen brought to a hydrogen ion concentration to a pH of about 3, will pass at room temperature (about C.) within a few minutes into a white crumbly cake unfit for anything. But the reaction will turn outquite dif-- ferently, if the urea is without any other modifi- 55 cation of the operating" conditions entirely or partly replaced by thiourea. If, for instance in the above specified starting mixture half of" the 60 parts by weight of the urea, that is parts.

be interrupted at a stage, in whichthe simple -chemical compounds metlr'vlol urea and dimethylol urea (or mixtures of these compounds) are formed, which do not yet show any tendency to polymerization, but are capable of further condensation. Now I have succeeded in breaking.

.the continuity of the reaction in the condensation of thiourea (or mixtures of thiourea and urea) ,with formaldehyde, by operating in an acid solu-- tionwithout heating. By this wayof proceedingflrst of all -true solutions of simple chemical compounds are produced, whereas the reaction between urea and formaldehyde, as has been mentioned above, will under the same conditions proceed without interruption up to the formation of useless insoluble masses. In the acid solution of the firstly generated Esimple thiourea (or thiourea and urea) formaldehyde condensation products the formation of complex compounds capable of polymerization and a slow,-

ly progressing polymerization will take place,

during which the condensation products are, by

growing of the molecules, successively trans-.

formed into the colloidal state. These reaction products can therefore, by systematically conducting the reaction, be brought into a state of polymerization which is adjusted to convenience, that is to say lower or higher, but in any case uniform. In addition thereto the colloids finally formed by this process are hydrophobe, so that they will give off the water easily and completely.

By other workers the interaction of thiourea and formaldehyde, when effected in an acid medium and without applying heat, has been found to yield a crystalline condensation. product of the composition CaH4N2S which is-said to be insoluble in all solvents and to be decomposed, with brownmg and eflfervescence, at about 202-203. This compound is a dimethylene-thiocarbamide which .does not have the character of artificialresins and does not pass over into such resins when being heated, but on the contrary is decomposed I.

by heat with or without the action of pressure,

and therefore cannot be used for the productionof artificial masses. It was learned from experimental work that the reaction takes this turn when the hydrogen ion concentration exceeds a certain limit, but this limit depends also on the proportion of thiomea present when the starting material is a mixture of ureaand thiourea, and on the temperature. Consequently. only the rule may be given concerning the hydrogen ion concentration fit for the present process, that the condensation has to be effected at a pH less .than5, and that there is an upper limit givin rise to the generation of the said methylenecompound and that in the present process the hydrogen ion concentration has to be adjusted so,as to lie between these two limits.

For manufacturing laminated sheets, the base material (paper or fabric) is in the form of sheets or of endless bands impregnated with the solu-' tions of the condensation products, to which, if required, filling materials, coloringsubstances or pigments may be'added. The solution applied to thematerial in this is then preferably evap- 2s orated also without heating, whereafter a. suitable number of such layers, one laid upon the other,

I are in the usual manner by the actionof heat I and pressure united and soto say welded together. I

The non-filled material is translucent and may becolored or streaked in any shade. The material can be bored, flied, milled, polished and inthe warm state also easily stamped. Its mechanical strength is very great, various objects, articles,

# pieces and parts exposed to considerable mechanical strain may be made therefrom such asfor instance parts of gearings, toothed wheels, highly strained parts of textile and other machines, centrifugal pots for spinning machines etc. I Likewise 40 they are adapted for manifold use in eiectrotechnics (low and high voltage technics,heavycurularly in high frequency technics) v fact that the dielectric power factor of these products depends to a very low degree upon the temperature, they are also particularly suited for the construction of transformers. Moreover as they are insensitive to water, alkalies and acids.

these nice looking materials can be used to a large extent for the manufacture 'of many I articles of daily use, furniture etc. and finally also for building. stitute' for'veneers of hitherto unequalled chemical propertiesmay be made therefrom, which for gg'itself-or in combination .with other materials '(suchasiron) maybeusedformanufactlu'ingfurniture and is also most appropriate as a cover for walls A special advantage of these products consists win thatthe structureof thepaper or thetissue (other. than asbestos) disappears nearly completely, so that, in contradistinction t0 thelaminated sheets made by means of phenol-formaldehyde condensation products, the have in 05 all directions the same structure and are therefore more resistant in chemical as well as in me- .chanical respect. The products are forinstance not liable to sp'littingand-for this reason can be ,f used for more purposes and 'to a greater extent than the hitherto known materials. 2

Examples (1)- 76 kilograms 1(1 mol.) of thiourea are ina finely powdered state under agitation dissolved 76 in 300 kilograms ofan aqueous formaldehyde so- Thus for instance a sublution containing 30 per cent by weight (3 mole) of formaldehyde. Then ,5 to 1 kilogram of phos-' phoric acid and 60 kilograms (1 moi.) of urea are added to this solution. Now paper or fabric of linenor asbestos is in a suitable manner impregnated with this solution and then kept during 24 hours at room temperature, during which time the excess of water dries oif. The impregnated single sheets may now be further worked up by any laminated sheets from phenol-formaldehyde condensation productafl For producing plates or blocks the sheets, a suitable number of which is superposed one upon'the other, are at a temmethod usually employed in the manufacture of perature of to C. pressed togetheni made according to Examplefll topartlcles of a size of about 1 centimeter'andhot the disintegrated mass underhigh preuure molded pieces of particularly high mechanical strength can be made. For this mode of carrying -out the.

process especially laminated linen sheets are most appropriate.

The process may also be carried outby'causing preliminarily prepared monbmethylol or dimethylol 'urea (or. mixturesof these compounds) to take part in the condensation of thiourea and formaldehyde under above specified conditions. The proportion of femaldehydehasin suchcase of courseto be diminished I for the amount belonging to the urea portion. rent and communication englneeringandpartic- Owing to the What I claim is:.-'

1.-'.lhe process of making tough; hard a.

dense sheets which comprisesimmlting-a celan aqueous medium which is more than cn=1o#' and lessacid than about Caf=10-.. drying the impregnated lamina without heating-the same, and subjecting the same thereafter'to pres-- product therein. 2. The process of y-making tough, hard and dense sheets which comprises impregnating a sure and'heat sumcientto form a *cellulosic lamina w'ithva solutionv prepared by mixing 1 mol. of a mixture of-thiourea and urea with less than-2 mois of formaldehyde in an aqueous "medium which is more acid than =1.o. and less me than about Ca=10-3, the:

mixing and impregnation. being accomplished without addition ofexte'rnal heat and the amount of thioureaf in the mixture being sufficient to prevent the formation of white insoluble formaldehyde-urea. products, drying the lamina without heating the same, "and thereafter subjecting the same and heat suillcient-toeflect the formation ofahydrophobe resinous compound therein. I

3. The process ofmaking twgh hardand dense sheets which ima cellulosic lamina with a solution prepared by mixing 1mol.ofamixtureofthioureaandureawithless.

than 2 mois of formaldehyde in an aqueous medium having .a hydrogen-ion of about Cn=l0-=, the mixing and impregnation being accomplished without addition of external heat and the amount of thiourea in the mixture being sumcient to prevent the formation of white insoluble formaldehyde-urea products, drying the impregnated cel iulos'io lamina without heating, the same, and thereafter subjecting the same to tical with that in claim 1.

5. A tough hard dens tical with that produce in claim2.

produced by the process set forth e sheet substantially idend by the process set forth 6. A tough hard dense sheet substantially identical with that produced by the process set forth in claim 3.

KURT arena. 

